This invention relates to heat pumps and, more particularly, to the use of chemical heat pumps for converting and storing solar energy, making solar energy a practical source for heating and cooling residential or commercial structures. It also relates to the solar collector used with the heat pump.
Absorption refrigeration systems for the purpose of storing thermal energy are known. My prior U.S. Pat. No. 3,642,059, issued Feb. 15, 1972, shows a particularly efficient small-scale absorption system used for refrigeration purposes and also for heating purposes on a stored energy basis. This system has not, however, in the past been designed in the form required for converting and storing solar energy for large-scale space heating or other purposes. In addition, these systems have not been used as combination heat pumps and heat storage systems, which are periodically regenerated to effectively apply cyclically available solar energy for such heating applications. Space heating, of course, requires substantial energy levels to be produced over extended periods of time. In addition, the space heating problem is cyclic, generally occurring on a 24-hour cycle, which requires daily use and may require daily regeneration of the heat pump system.
Prior absorption refrigeration systems have not been designed which would satisfactorily operate to store and convert energy in this environment. One of the more important factors limiting the effectiveness of prior systems based on powdered absorbants has been the fact that, because of the low vapor pressures within the containers generally required for their satisfactory operation, the containers have generally been built as relatively heavy and expensive rigid structures. During absorption and desorption, the vapor-absorbant powder expands and contracts physically. This size change (particularly after numerous cycles of absorption and desorption), tends to lift the chemical from the container walls and to produce voids within the powder bed. Since the container walls are used for the purpose of heat transfer, these resulting evacuated voids between the chemical and the container wall and throughout the powder significantly reduce the effectiveness of the system.
Solar systems in the past, particularly those which use flat plate collectors without concentrators (and especially those in which the flat plate collector is left at a single orientation year around), have suffered from substantial heat losses to the environment, even though one or more layers of transparent material were used to cover the absorbing surface. Normally, in such systems the layers of air between the transparent plates have been static. The static air present between the transparent layers in prior systems has, through convection, conducted heat to the ambient, which significantly reduces the overall efficiency of the solar collection system.
The usual method considered in prior systems of storing solar energy for use during nighttime hours has been either through the sensible heat of water or other material, with satisfactory heat capacity or through the heat of fusion of salts. The prior systems require substantial size and weight, and usually are not feasible for rooftop installation. Prior similar solar systems have not incorporated a heat pump which permits the utilization of heat extracted from the atmosphere to enhance the efficiency of alternate heat sources, such as fossil fuel sources, which must be used during periods of extended cloudiness.